The present invention relates to cylindrical-type wastewater screens and more particularly to a sprayer for cleaning the cylindrical screen during operation.
Presently, wastewater is a byproduct of many industrial processes that use water. For example, the food industry relies rather heavily on water for processing food. Water is used to clean vegetables, beef, fish, poultry, and other types of food often before the food is cooked, blanched or sterilized using other water. Unfortunately, after all this water is used it typically must also be processed to clean it so it can be either reused or inexpensively disposed. As a result of rather restrictive environmental laws and regulations that have made disposal of unprocessed wastewater prohibitively expensive, wastewater processing or preprocessing at the site of the food processing facility is desirable.
One apparatus that has proved particularly effective at treating wastewater is a cylindrical-type wastewater screen and such is shown and described in my U.S. Pat. No. 5,433,849, issued Jul. 18, 1995. As shown in that patent, a cylindrical-type wastewater screen has a cylindrical screen, typically comprised of perforate wedgewire, into which the wastewater is introduced while the screen is rotated. The wastewater passes radially outwardly through the screen after which it can be reused, further filtered, or disposed. Solids entrained in the wastewater that were filtered out of the wastewater can be cheaply disposed of as landfill or fertilizer. As shown, two cylindrical-type screens having successively finer screen media can be concentrically arranged to provide staged treatment of wastewater.
During operation, wastewater introduced within the cylindrical screen passes radially outwardly through perforations in the screen while most of the solids entrained in the wastewater is filtered by and retained in the screen because the perforations typically are no greater than about ten to twenty thousandths of an inch. The filtered solids often cling to the screen and the screen is rotated to cause gravity to encourage the solids to separate from the screen and fall to the bottom of the screen. A small flow of wastewater at the bottom of the screen carries the solids from the screen helping to keep the screen clean.
Many times, sticky solids, such as fat, connective tissue, coatings, starch, and other sticky residue will continue to cling to the screen despite rotation of the screen. The sticky solids can also cause other solids in the wastewater to stick to it and in general will significantly reduce the efficiency of the screen by partially or completely plugging perforations. Should too many perforations become plugged, the screen will have to be taken offline and cleaned.
Presently, to help keep the screen clean to prevent too many perforations from becoming plugged, fixed or stationary nozzles carried by a manifold which is disposed adjacent the screen can discharge cold water, hot water, steam or even air forcefully against the screen. Several spaced apart nozzles must be used to clean the screen along its entire axial length. Unfortunately, where water is used, each nozzle typically requires a flow of as much as about 3 gallons per minute such that a typical screen can use as much as 30 to 90 gallons of water per minute, depending on the number of nozzles required and the type of screening apparatus used. For example, where a double cylinder wastewater screen is used, such as is disclosed in U.S. Pat. No. 5,433,849 to Zittel, as many as 30 nozzles fixed to at least two manifolds are used to keep both cylinders clean. While the frequency of cleaning can vary with the type of solids entrained in the wastewater, each cleaning cycle nonetheless uses a lot of water which undesirably increases wastewater treatment costs.
While reciprocating sprayers have been used in some types of similar processing equipment, they have not been viewed as particularly well suited for use in cylindrical-type because of reliability considerations and because of concern they could not effectively clean the rather small perforations found in wastewater screens. For example, it is known to use a reciprocating sprayer to direct water against a perforate cylinder of a bean snipper to free the perforations of bean parts that have become lodged in them. However, the perforations in the cylinder of a bean snipper are much larger, typically at least {fraction (13/64)} (0.203) of an inch, the cylinder is made of polycarbonate, and a bean snipper is used to cut beans, not process wastewater. Moreover, it is not believed that the reciprocating sprayer used in bean snippers discharges water at a great enough pressure to completely pass through the exterior of the screen adjacent the sprayer and impact against the interior of the screen on the opposite side. Additionally, reciprocating sprayers can incorporate a rodless air cylinder system that uses an air cylinder. Such a system can require a sufficiently clean supply of air that may not be available at a plant utilizing a reciprocating sprayer.
The present invention provides an apparatus for screening wastewater. The apparatus for screening wastewater includes a frame, a rotatable cylindrical screen carried by the frame and having an axis of rotation and which is defined by a tubular perforate wedgewire sidewall having an interior wedgewire surface and an exterior wedgewire surface, and a wastewater conduit having an opening disposed inside the wedgewire sidewall through which conduit effluent is discharged. The apparatus for screening wastewater further includes a plurality of spray nozzles positioned along the length of the cylindrical screen from which fluid is ejected against the wedgewire sidewall to dislodge solids from the wedgewire sidewall, a control system coupled to the plurality of spray nozzles that controls the order that each nozzle of the plurality of spray nozzles ejects fluid and controls a duration of time that each nozzle of the plurality of nozzles ejects fluid, and a pump in fluid flow communication with a supply of the fluid for delivering the fluid to the plurality of spray nozzles.
The plurality of nozzles can eject fluid under pressure sufficient to impinge against and pass through the outer surface of the wedgewire sidewall and then impinge against an inner surface of the wedgewire sidewall such that solids are dislodged at both regions of impingement. The plurality of spray nozzles can also eject fluid at a pressure of at least about 80 to 1000 psi. The plurality of spray nozzles can additionally eject fluid at a volume of about 5 to 20 gallons per minute based on the size of the screen and based on the water pressure supplied. The wedgewire sidewall of said cylinder can have openings of 10 to 20 thousands of an inch.
The apparatus for screening wastewater can further include a second cylindrical screen that is comprised of a tubular perforate wedgewire sidewall wherein the fluid from the plurality of spray nozzles is under sufficient pressure that it impinges against and passes through the outer surface of the cylindrical screen, the outer surface of the second cylindrical screen, the inner surface of the second cylindrical screen, and the inner surface of an opposite side of the cylindrical screen. The sprayer can be disposed about 4 to 6 inches away from the outer sidewall of the cylindrical screen. The plurality of spray nozzles can be arranged so that the fluid ejected from the spray nozzles against the wedgewire sidewall provides complete coverage of the cylindrical screen along the axis of rotation.
The apparatus for screening wastewater can further include a plurality of electrically actuated valves coupled to the plurality of spray nozzles positioned along the length of the cylindrical screen, wherein the controller can control the operation of the electrically actuated values to provide fluid to the plurality of spray nozzles. The valves can open and close in sequence to eject fluid from the spray nozzles to sequential areas of the cylindrical screen.
The apparatus for screening wastewater can further include a plurality of spray manifolds coupled to the plurality of spray nozzles, wherein each of the plurality of spray manifolds can be coupled to at least one of the plurality of spray nozzles. The apparatus for screening wastewater can further include an operator interface coupled to the control system.